Added parenthesis in TBigInt.ToString for negative values

UBigInt.pas

@@ -532,7 +532,7 @@ var
   i: Integer;
 begin
   if FIsNegative then
-    Result := '-'
+    Result := '(-'
   else
     Result := '';
   for i := 0 to Length(FDigits) - 2 do
@@ -540,6 +540,8 @@ begin
   Result := Result + IntToStr(FDigits[Length(FDigits) - 1]);
   for i := 0 to Length(FDigits) - 2 do
     Result := Result + ')';
+  if FIsNegative then
+    Result := Result + ')'
 end;
 
 class function TBigInt.FromInt64(const AValue: Int64): TBigInt;